GaN’s Bright Future

GaN-on-Si is moving towards becoming a cost-effective enabler for next-generation LED and power devices.

During the past decade gallium nitride (GaN) has become an important compound semiconductor as it enables numerous key applications in optoelectronics and in power electronics.

GaN LED technology could well be the Holy Grail in terms of providing the next generation of lighting. LEDs in general present many advantages over incandescent light sources, including a higher luminous efficacy in combination with a longer lifetime.

Power SiN/AlGaN/GaN transistors mounted on AlN ceramics.

Within the LED family, GaN is the only material that enables fabrication of efficient blue and white LEDs. Today, InGaN/GaN based blue, green and white devices are already available on the LED market – which is a multi-billion euro high-volume market.

In power electronics, the GaN materials system enables the fabrication of power components that offer a competitive advantage to traditional silicon MOSFET power devices. GaN intrinsically possess an electrical breakdown field that is 10 times larger than silicon, while offering excellent transport properties: key enablers for very effective reductions of both conduction and switching losses at high voltages or for high-power/high-frequency operation. Due to its wide band gap (3.4eV), operation at high temperatures is no longer an obstacle.

All these characteristics make the material especially suited for fabricating the next-generation of switching components to be used in electric motors, power invertors or DC/DC convertors, for example. And although GaN technology for these applications is still in its infancy, the market for such switching components is destined to grow considerably, because of the drive to use more hybrid electrical vehicles in transport, more solar installations, more wind farms, and the smart grids to connect it all.

Reigning in costs

But today, GaN technology is still very expensive. Lower costs and greater productivity consistency are prerequisite for a further widespread acceptance by industry.

Measuring an InGaN/GaN based LED.

One way to address this concern is to bring GaN LED and power manufacturing processes towards a production platform that uses a CMOS-like process on 8-inch silicon wafers. Today, GaN processes are typically performed on smaller size substrates, such as the very expensive silicon carbide (SiC – for power and RF electronics) and sapphire (for LEDs) substrates, predominantly available in diameters of 2, 3 or 4 inches.

At imec, we are convinced of the tremendous advantages of using 8-inch silicon substrates in an 8-inch silicon facility: up-scaling the wafer size increases the productivity and hence the cost-efficiency, as more chips become available for an equal amount of fabrication steps. But we can also benefit from the many years of high-volume silicon manufacturing know how.

For example, for LED manufacturing, the availability of process and particle control, in-situ metrology and accelerated lifetime testing facilitates the production of highly reliable devices with long lifetime that are highly uniform in terms of light intensity and wavelength. In other words, we will achieve lower cost by leveraging the ‘economies of scale’ of silicon.

At imec, we tackle these challenges in our industrial affiliation program (IIAP) on GaN power and LED devices, together with our program partners. This IIAP builds on imec’s excellent track record in GaN epi-layer growth, new device concepts (e.g. HEMTs, double HEMTs, e-mode devices) and CMOS device integration. We are on track in making these GaN processes silicon compatible and, meanwhile, we are developing GaN epitaxy on 8 inch in a new epi reactor – important steps towards the fabrication of cost-effective next-generation GaN devices.

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